A new multi-gas constrained model of trace gas non-homogeneous transport in firn: evaluation and behaviour at eleven polar sites

Witrant, E.; Martinerie, P.; Hogan, C.; Laube, J.C.; Kawamura, K.; Capron, E. ORCID: https://orcid.org/0000-0003-0784-1884; Montzka, S.A.; Dlugokencky, E.J.; Etheridge, D.; Blunier, T.; Sturges, W.T.. 2012 A new multi-gas constrained model of trace gas non-homogeneous transport in firn: evaluation and behaviour at eleven polar sites. Atmospheric Chemistry and Physics, 12 (23). 11465-11483. 10.5194/acp-12-11465-2012

Before downloading, please read NORA policies.

Preview

Text acp-12-11465-2012.pdf - Published Version Download (1MB) | Preview

Abstract/Summary

Insoluble trace gases are trapped in polar ice at the firn-ice transition, at approximately 50 to 100 m below the surface, depending primarily on the site temperature and snow accumulation. Models of trace gas transport in polar firn are used to relate firn air and ice core records of trace gases to their atmospheric history. We propose a new model based on the following contributions. First, the firn air transport model is revised in a poromechanics framework with emphasis on the non-homogeneous properties and the treatment of gravitational settling. We then derive a nonlinear least square multi-gas optimisation scheme to calculate the effective firn diffusivity (automatic diffusivity tuning). The improvements gained by the multi-gas approach are investigated (up to ten gases for a single site are included in the optimisation process). We apply the model to four Arctic (Devon Island, NEEM, North GRIP, Summit) and seven Antarctic (DE08, Berkner Island, Siple Dome, Dronning Maud Land, South Pole, Dome C, Vostok) sites and calculate their respective depth-dependent diffusivity profiles. Among these different sites, a relationship is inferred between the snow accumulation rate and an increasing thickness of the lock-in zone defined from the isotopic composition of molecular nitrogen in firn air (denoted δ15N). It is associated with a reduced diffusivity value and an increased ratio of advective to diffusive flux in deep firn, which is particularly important at high accumulation rate sites. This has implications for the understanding of δ15N of N2 records in ice cores, in relation with past variations of the snow accumulation rate. As the snow accumulation rate is clearly a primary control on the thickness of the lock-in zone, our new approach that allows for the estimation of the lock-in zone width as a function of accumulation may lead to a better constraint on the age difference between the ice and entrapped gases.

Item Type:	Publication - Article
Digital Object Identifier (DOI):	10.5194/acp-12-11465-2012
Programmes:	BAS Programmes > Polar Science for Planet Earth (2009 - ) > Chemistry and Past Climate
ISSN:	1680-7324
Additional Information. Not used in RCUK Gateway to Research.:	A supplement to this article is available at http://www.atmos-chem-phys.net/12/11465/2012/acp-12-11465-2012-supplement.pdf This work is distributed under the Creative Commons Attribution 3.0 License together with an author copyright. This license does not conflict with the regulations of the Crown Copyright.
NORA Subject Terms:	Chemistry
Date made live:	05 Feb 2013 11:55 +0 (UTC)
URI:	https://nora.nerc.ac.uk/id/eprint/21412

Actions (login required)

View Item

Document Downloads

More statistics for this item...